Image pickup devices are usually used to take photographs or record video data. In addition, image pickup devices are applied to web cameras for holding a video conference. Recently, the commercially available notebook computer is usually equipped with a built-in image pickup device.
With increasing development of digital techniques, text documents are gradually created as electronic files. Generally, text documents are scanned by scanning apparatuses and then saved as electronic files such as PDF (Portable Document Format) files. In a case that no scanning apparatus is communicated with the notebook computer, the images of simple documents such as single-sided papers or business cards may be captured by the built-in image pickup device. The images captured by the built-in image pickup device are usually saved as JPEG (Joint Photographic Experts Group) files. Most users prefer using scanning apparatuses to scan the text documents as PDF files because the texts and signs contained in the PDF files are readable by the computer systems and may be converted as editable text files.
As known, optical character recognition (OCR) is a process of capturing an image of a document and then extracting the texts from that image. It is possible to analyze images that are captured from the image pickup device according to the OCR technique and saved as JPEG files. As a consequence, individual texts or signs contained in the JPEG files are recognized and converted as editable text files. Since the associated OCR techniques are well established, the image pickup device is gradually adopted to obtain electronic files of the documents.
Take a notebook computer having an image pickup device for example. The image pickup device is usually arranged on an upper cover of the notebook computer. After the document is placed on a proper location of a working plane (e.g. a desk plane), the upper cover of the notebook computer is rotated such that the image pickup device is aligned with or close to the document. Meanwhile, the image of the document may be captured by the image pickup device. When the image pickup device of the notebook computer is used to capture the image of the document placed on the working plane, some drawbacks also occur. The common drawback is occurrence of a distorted image. Since there is no reliable reference point on the document of the working plane, the location of the document on the working plane is readily deviated from the previously adjusted location. Such deviation may cause defocus aberration of the image pickup device during the image capturing process. Under this circumstance, the obtained image is usually blurred. Furthermore, since the shooting range of the image pickup device is insufficient to cover a relatively large-sized document, the image of the large-sized document that is captured by the image pickup device for a single time is usually incomplete. For solving this drawback, the user usually shoots the document for two times in order to obtain two incomplete images. By means of image processing techniques, these two incomplete images are combined together. In other words, after the upper-half portion of the document is captured by the image pickup device, the document should be moved until the lens of the image pickup device is aligned with the lower-half portion of the document and then the image of the lower-half portion is captured. Since there is no reliable reference tool or reference point on the document, the document is readily aslant during movement of the document. The aslant document usually fails to be parallel with or located at the original location of the document. Under this circumstance, the image of the lower-half portion of the document is distorted and is unsuccessfully combined with the upper-half portion of the document. For obtaining a sharp image, it is necessary to re-shoot the document. In other words, it is troublesome for the user to correct the distorted image.
Therefore, there is a need of providing a method of capturing a sharp and non-distorted image so as to obviate the drawbacks encountered from the prior art.